1. Field of the Invention
The present invention relates generally to a flow control valve and, more particularly, to a valve especially suited for use as a water faucet wherein the valved fluid assists in effecting a fluid-tight seal and wherein significant components of the valve form an easily replaceable cartridge.
2. Description of the Prior Art
Various forms of flow control valves or faucets have been developed for residential and other use to deliver fluids such as water. The need to frequently replace wear items in flow control valves has been a persistant problem. Individuals unfamiliar with plumbing work often encounter difficulties in effecting proper repairs and/or replacements of the defective components.
In a typical prior valve, a brase valve seat is included as part of the inlet section of the valve. An elastomeric washer is affixed to an elongate, threaded stem having an upwardly projecting handle portion. A packing surrounds the stem to prevent leakage. Upon rotation of the handle, the stem is advanced axially within the valve and the washer is advanced into or out of engagement with the valve seat. If the handle is tightened too much, the washer will be compressed to the point where its yield stress will be exceeded and the washer will adopt an undesired "set. " This is a permanent deformation of the washer which eventually will lead to a leak. It is difficult to consistently tighten the handle so that waterflow is prevented and yet the yield stress of the washer is not exceeded.
The foregoing problem is made more difficult because of the type of contact which is created between the valve seat and the washer. In a typical valve, the washer is rigidly secured to the end of the stem. Accordingly, the washer is rotated as it is advanced into contact with the valve seat. The resultant frictional engagement with the valve seat abrades the washer and eventually causes it to wear to the point where a leak will occur. This problem increases with the passage of time because brass valve seats gradually deteriorate due to chemical reaction with water. The valve seats eventually lose their initial smooth surface and this leads to increased abrasion of the washers.
Yet additional problems exist then replacement of a washer is necessary. The washers often are difficult to remove from the end of the stem. Screws holding the washers in place may corrode, may become difficult to remove, and may break during attempted removal. It also is important that a replacement washer of the proper size, shape, and material be provided. This presents a challenge to the user who procures washers individually in order to repair various valves. Moreover, the "ever leaking" packings used to seal stems against leakage may be damaged during valve disassembly and reassembly with the result that leakage subsequently may occur around the stem.
In response to the foregoing concerns, several approaches have been suggested. One approach has been to avoid sliding contact between the washer and the valve seat in order to prevent frictional degradation of the washer. Either the stem is supported for non-rotating axial displacement toward and away from the valve seat, or the washer is rotatably secured to the stem so that, upon tightening of the stem, the stem rotates with respect to the washer, but the washer is fixed with respect to the valve seat. Although these approaches represent an improvement over more conventional valve constructions, they still fail to control the extent to which the washer is compressed. Consequently, it still is possible to "set" the washer and cause the valve to leak.
An approach which has had some success is to provide a power assist to the valve element during valve closure. The thought underlying this approach is that the user will be less likely to overtighten the washer if an assist is provided uring the closure process. For example, the valve may be a normally closed valve in which the valve element is biased toward a closed position by a spring or even by the pressure of the valved fluid itself. In one valve, a lost motion connection between the stem and the valve element attempts to eliminate excessive closure force as a problem. Although the basic idea of a closure assist is sound, it still has been difficult to replace components of closure-assisted valves although, of course, replacement of such components is needed less often than in non-closure-assisted valves.
In order to ease replacement difficulties, components of valves subject to wear have been provided in cartridge form. A cartridge is thought to be easier to remove and replace than individual components of a conventional valve. Because the components subject to wear are included as part of the cartridge, insertion of a new cartridge generally does not involve any significant concern about establishing sealing contact between movable components of the valve structure. The sealing concerns that do exist are relatively easily dealt with by the use of O-rings or other commonly used self-sealing members.
Although valves having power-assisted closures between nonrotating washers and valve seats included as parts of cartridges already are known, certain considerations still have not been addressed. One of these considerations relates to the nature of the closure assist. In one known valve, a spring has been used to carry and bias a vitreous valve element toward engagement with a valve seat. The spring is flexible and misalignment between the valve element and the valve seat is made possible. Also, the flexible nature of the spring can lead to "chatter" as the valve element is advanced toward a valve closed position. Further, as the spring begins to sag or take a set, the valve element will fail to effect a closure.
Another problem not addressed by prior carytridge valve proposals is that of providing a good seal between a movable stem and the cartridge without the use of a packing. Even though the threads of the stem may be tightly mated with threads in the cartridge, packing material of some kind still is needed.
Yet another problem not adequately addressed by prior cartridge valve proposals is that of permitting cartridge components to be manufactured inexpensively. Preferably the components will be long-lived plastic members capable of manufacture in an inexpensive molding process. It is desired that the cartridge employ a minimal number of complexly configured portions in order to decrease manufacturing expense and avoid the need to closely control production tolerances.